The pinhole test was used to determine the boundaries between dispersive and nondispersive behavior for a clay shale with respect to acidity and salt concentration in the erosion solution. It was found that, for this soil, a decrease in pH of the eroding water to less than about 4 (using hydrochloric acid) or an increase to greater than about 11 (using calcium hydroxide or sodium hydroxide) caused a change from dispersive to nondispersive behavior. Similarly, increasing the salt concentration of the eroding water at its natural pH of 6.3 to 0.1 N calcium chloride or 0.5 N sodium chloride caused erosion to stop.